We have continued our studies on a human lung tumor-associated antigen (LTA) which can be demonstrated in 86% of extracts of lung tumors of all major histological types but not in extracts of other tumors, normal adult or fetal lung and other normal tissues. LTD does not appear to be related to other tumor-associated antigens. Efforts during the last year have primarily been directed at improving a radioimmunoassay (RIA) and developing a purification scheme for LTA from a tissue culture cell line (ChaGo). The RIA has been considerably improved by treating radioiodinated LTA with Pansorbin prior to use in the assay. This RIA was used to test a panel of 215 sera. A cutoff of 1.7ng/ml (2 SD above the mean) was selected based on 88 normals, above which 2/88 normals, 0/24 benign lung disease and 3/23 patients with cancer other than lung were found. In the lung cancer group, 13/31 squamous (42%), 9/15 adeno (60%), 3/18 large and 3/16 small cell carcinoma patients were positive. To continue these studies we developed a purification procedure of LTA from ChaGo which yields nearly homogeneous antigen.